Screens for exhibiting projected images typically comprise a substrate or support structure plus some overlaying coating which comprises a screen surface. The present invention is directed to problems associated with the screen substrate or support structure; for the rest of the present application, unless otherwise noted, the screen is defined as the structure minus the surface coating. It is understood that any one of many surface coatings, well known in the art, can be employed with the screen structure of the present invention.
Screens for exhibiting projected images have been provided with curvatures in their horizontal and vertical directions. When the dimensions of the surface of the screen are small, the structure which supports the screen surface can provide rigidity without becoming unwieldly.
Situations exist, however, where it is necessary to employ large screens.
One area that requires large screens is the field of flight simulation. Flight simulation is the generalized term given to the situation where pilots are given on-the-ground training in how to fly aircraft.
Typically, the flight simulator pilot is seated in the middle of a large, geodesic dome structure. An image projection system is used to present a highly realistic visual background environment for the flight simulator pilot. The screen for the image projection system is the interior surface of the geodesic dome. A typical arrangement will employ image projection screens having curvatures of approximately 230" radius.
To make such large screens, two basic interdependent problems must be identified and simultaneously solved.
The first basic problem concerns structure. The structure provides the background support and rigidity for the screen surface. A large screen must have support structure of sufficient integrity and rigidity so that it does not collapse upon itself. Essentially, all the rectilinear forces of the screen support structure must be balanced.
One approach that can be utilized in order to provide structural strength and integrity for a large screen consists in connecting together curvilinear screen segments. Curvilinear screen segments are similar curvilinear units or building blocks which are connected together to build up a larger curvilinear screen.
However, the process of segmenting a large screen introduces an auxiliary problem. The auxiliary problem resides in the necessity of balancing all of the torques that are introduced by connecting together curvilinear segments into a curvilinear screen structure. If the torques are not balanced, the structure will collapse upon itself. Also, unbalanced torques will usually result in warpage and buckling between screen segments.
In summary, the first basic problem in making a large segmented curvilinear screen consists in balancing and resolving the structural rectilinear forces and torques.
The second basic problem in making a large, segmented curvilinear screen concerns curvature. For effective image projection, a screen surface must be continuous and smooth.
A large, segmented curvilinear screen cannot have discontinuities of curvature. Discontinuities of curvature will arise from undulations, warpage or irregularites on the screen surface. Discontinuities which look like seams also arise along the line of intersection of two screen segments.
Discontinuity of curvature will result in non-effective image projection. An example which illustrates the adverse effects of discontinuity of curvature is provided by the image projection system described above in conjunction with flight simulation.
If there is a discontinuity of curvature, a flight simulator pilot will initially assume that undulations on the screen surface are "clouds." When motion is introduced into the visual system, the pilot will observe that the "clouds" move with him, instead of receding into the background. The pilot will be mislead due to discontinuity of curvature.
In order to minimize the discontinuity of curvature problem, it has been found that the viewing surface of the projection screen of a flight simulator should show deviations in curvature less than 0.010 in/1 inch.
The first basic problem (structural forces and torques) and the second basic problem (curvature) are interdependent problems in large screen construction.
Successful large screen construction comprehends the interdependent problem from the outset, and from this vantage point, provides a solution that simultaneously address the problems of structure and curvature.
The prior art is not fully cognizant of the implications of the interdependent problem. Thus, one can observe a tendency in the prior art to first satisfy the difficult problems of balancing rectilinear and torque forces without due consideration for the curvature problem. In the prior art, one method presented is that of building a large structure, and then trying to "fine-tune" the curvature by locally forcing one segment to conform to its neighbor. The problem with this is that once the "fine-tune" adjustments are made over a small area of segments, the large structural rectilinear and torque forces are thrown out of balance. Thus, the entire process of "fine-tuning" must begin anew. A never ending vicious cycle is thus presented.
The Hourdiaux U.S. Pat. No. 3,348,897 illustrates the case where "fine-tuning" of curvature is attempted. Hourdiaux describes a screen built of panels which are assembled and clamped against each other. A curvature control device for "fine-tuning" the curvature is provided. This device comprises an intricate set of connecting rods which have opposite screw-threaded portions engaging internal opposite threadings of a common adjusting nut.
In the process of setting each clamp, structural rectilinear forces and torques are set into play. Hourdiauz does not show how the large screen is built up so that the structural forces and torques are balanced with the clamp curvature torques. A failure to balance these torques will give rise to either structural instability or discontinuity of curvature.
It is also unclear from the Hourdiaux design if the system allows for fine-tuning the curvature in the range 0.010 in/1 inch deviation as required for high quality image projection.
Besides the two basic interdependent problems of structure and curvature, additional problems must also be identified and solved in large segmented screen construction.
Large segmented screens must be easily and inexpensively assembled and disassembled for transport. In addition, the assembled screen should require a minimum of screen surface rework to insure smoothness and continuity.
Further, the image projection system of a flight simulator may be subjected to large motion forces. This acts to jostle the screen segments and the connections between screen segments. The result is that the continuity of curvature may not be maintained. Hence, the structure must be designed so that large motion forces are dissipated and the curvature of the screen viewing system is preserved.
Large screens may take a variety of geometric shapes and sizes. In the area of flight simulation, it is contemplated that a large geodesic dome be one such overall shape. Geodesic domes approach a spheriod shape. Other common practical shapes are ellipsoid, parabolic and hyperboilc. It follows that individual screen segments can have conic section or hyberbolic shapes.
Regardless of the particular chosen size or shape, it is necessary to have one method of construction that can be employed to make a large, segmented curvilinear screen.
The present invention successfully overcomes the shortcomings associated with the prior art. Moreover, it addresses and solves the additional problems present in large, curvilinear screen construction. With the apparatus of the present invention, structural forces and torques are balanced so that the screen has structural stability and the screen surface has a smooth, continuous curvature. The structure is provided with sufficient rigidity and resiliency to absorb motion forces. Moreover, the structure may be easily assembled and disassembled. Finally, a method of construction of the present invention allows diverse geometric screen segments to be utilized in building up a large, segmented curvilinear screen.